Nicholas B. Stephens

Human-like hand use in Australopithecus africanus

Getting a grip The evolution of the hand—particularly the opposable thumb—was key to the success of early humans. Without a precise grip, involving forceful opposition of thumb with fingers, tool technology could not have emerged. Skinner et al. analyzed the internal bone structure of Pliocene Australopithecus hands, dated at 3.2 million years old. Internal bone structure reveals the patterns and directions of forces operating on the hand, providing clues to the kinds of activities performed. Modern human-like hand postures consistent with the habitual use of tools appeared about half a million years earlier than the first archaeological evidence of stone tools. Science, this issue p. 395 The internal bone structure of Pliocene australopiths suggests that precision grip evolved 3.2 million years ago. The distinctly human ability for forceful precision and power “squeeze” gripping is linked to two key evolutionary transitions in hand use: a reduction in arboreal climbing and the manufacture and use of tools. However, it is unclear when these locomotory and manipulative transitions occurred. Here we show that Australopithecus africanus (~3 to 2 million years ago) and several Pleistocene hominins, traditionally considered not to have engaged in habitual tool manufacture, have a human-like trabecular bone pattern in the metacarpals consistent with forceful opposition of the thumb and fingers typically adopted during tool use. These results support archaeological evidence for stone tool use in australopiths and provide morphological evidence that Pliocene hominins achieved human-like hand postures much earlier and more frequently than previously considered.

Human-like hand-use in the hand of Australopithecus africanus

Getting a grip The evolution of the hand—particularly the opposable thumb—was key to the success of early humans. Without a precise grip, involving forceful opposition of thumb with fingers, tool technology could not have emerged. Skinner et al. analyzed the internal bone structure of Pliocene Australopithecus hands, dated at 3.2 million years old. Internal bone structure reveals the patterns and directions of forces operating on the hand, providing clues to the kinds of activities performed. Modern human-like hand postures consistent with the habitual use of tools appeared about half a million years earlier than the first archaeological evidence of stone tools. Science, this issue p. 395 The internal bone structure of Pliocene australopiths suggests that precision grip evolved 3.2 million years ago. The distinctly human ability for forceful precision and power “squeeze” gripping is linked to two key evolutionary transitions in hand use: a reduction in arboreal climbing and the manufacture and use of tools. However, it is unclear when these locomotory and manipulative transitions occurred. Here we show that Australopithecus africanus (~3 to 2 million years ago) and several Pleistocene hominins, traditionally considered not to have engaged in habitual tool manufacture, have a human-like trabecular bone pattern in the metacarpals consistent with forceful opposition of the thumb and fingers typically adopted during tool use. These results support archaeological evidence for stone tool use in australopiths and provide morphological evidence that Pliocene hominins achieved human-like hand postures much earlier and more frequently than previously considered.

Trabecular architecture in the thumb of Pan and Homo: implications for investigating hand use, loading, and hand preference in the fossil record

OBJECTIVES Humans display an 85-95% cross-cultural right-hand bias in skilled tasks, which is considered a derived behavior because such a high frequency is not reported in wild non-human primates. Handedness is generally considered to be an evolutionary byproduct of selection for manual dexterity and augmented visuo-cognitive capabilities within the context of complex stone tool manufacture/use. Testing this hypothesis requires an understanding of when appreciable levels of right dominant behavior entered the fossil record. Because bone remodels in vivo, skeletal asymmetries are thought to reflect greater mechanical loading on the dominant side, but incomplete preservation of external morphology and ambiguities about past loading environments complicate interpretations. We test if internal trabecular bone is capable of providing additional information by analyzing the thumb of Homo sapiens and Pan. MATERIALS AND METHODS We assess trabecular structure at the distal head and proximal base of paired (left/right) first metacarpals using micro-CT scans of Homo sapiens (n = 14) and Pan (n = 9). Throughout each epiphysis we quantify average and local bone volume fraction (BV/TV), degree of anisotropy (DA), and elastic modulus (E) to address bone volume patterning and directional asymmetry. RESULTS We find a right directional asymmetry in H. sapiens consistent with population-level handedness, but also report a left directional asymmetry in Pan that may be the result of postural and/or locomotor loading. CONCLUSION We conclude that trabecular bone is capable of detecting right/left directional asymmetry, but suggest coupling studies of internal structure with analyses of other skeletal elements and cortical bone prior to applications in the fossil record.

Homo sapiens in Arabia by 85,000 years ago

Understanding the timing and character of the expansion of Homo sapiens out of Africa is critical for inferring the colonization and admixture processes that underpin global population history. It has been argued that dispersal out of Africa had an early phase, particularly ~130–90 thousand years ago (ka), that reached only the East Mediterranean Levant, and a later phase, ~60–50 ka, that extended across the diverse environments of Eurasia to Sahul. However, recent findings from East Asia and Sahul challenge this model. Here we show that H. sapiens was in the Arabian Peninsula before 85 ka. We describe the Al Wusta-1 (AW-1) intermediate phalanx from the site of Al Wusta in the Nefud desert, Saudi Arabia. AW-1 is the oldest directly dated fossil of our species outside Africa and the Levant. The palaeoenvironmental context of Al Wusta demonstrates that H. sapiens using Middle Palaeolithic stone tools dispersed into Arabia during a phase of increased precipitation driven by orbital forcing, in association with a primarily African fauna. A Bayesian model incorporating independent chronometric age estimates indicates a chronology for Al Wusta of ~95–86 ka, which we correlate with a humid episode in the later part of Marine Isotope Stage 5 known from various regional records. Al Wusta shows that early dispersals were more spatially and temporally extensive than previously thought. Early H. sapiens dispersals out of Africa were not limited to winter rainfall-fed Levantine Mediterranean woodlands immediately adjacent to Africa, but extended deep into the semi-arid grasslands of Arabia, facilitated by periods of enhanced monsoonal rainfall.A directly dated Homo sapiens phalanx from the Nefud desert reveals human presence in the Arabian Peninsula before 85,000 years ago. This represents the earliest date for H. sapiens outside Africa and the Levant.

Response to Comment on “Human-like hand use in Australopithecus africanus”

Almécija and colleagues claim that we apply a simplified understanding of bone functional adaptation and that our results of human-like hand use in Australopithecus africanus are not novel. We argue that our results speak to actual behavior, rather than potential behaviors, and our functional interpretation is well supported by our methodological approach, comparative sample, and previous experimental data.

Signals of loading and function in the human hand: A multi-method analysis of the external cortical and internal trabecular bone of the metacarpals

Leprosy is one of the few specific infectious diseases that can be studied in bioarchaeology due to its characteristic debilitating and disfiguring skeletal changes. Leprosy has been, and continues to be, one of the most socially stigmatising diseases in history, over-riding all other aspects of social identity for the sufferers and frequently resulting in social exclusion. This study examines the stable isotopic evidence of mobility patterns of children, adolescents, and young adult individuals with the lepromatous form of leprosy in Medieval England (10 th –12 th centuries AD) to assess whether the individuals buried with the disease were non-locals, possibly from further afield. Enamel samples from 19 individuals from the St. Mary Magdalen Leprosy Hospital, Winchester (UK) were selected for strontium ( 87 Sr/ 86 6U DQG R[\JHQ į 18 O) stable isotope analysis based on age at death (<30 years), the presence of bone changes associated with lepromatous leprosy, and the underlying geology of their burial locations. The results from these data indicate that the St. Mary Magdalen Leprosy Hospital received an almost equal mixture of local and non-local individuals from further afield, including early pilgrims. At present, the St. Mary Magdalen Leprosy Hospital is the earliest dedicated leprosaria found within Britain and mobility studies such as these can help elucidate and test some of the broader historical notions and identities associated with the movements of those infected with the disease in Medieval England.

Predictions for an osteological signature of stone tool behaviors in hard tissue anatomy

Leprosy is one of the few specific infectious diseases that can be studied in bioarchaeology due to its characteristic debilitating and disfiguring skeletal changes. Leprosy has been, and continues to be, one of the most socially stigmatising diseases in history, over-riding all other aspects of social identity for the sufferers and frequently resulting in social exclusion. This study examines the stable isotopic evidence of mobility patterns of children, adolescents, and young adult individuals with the lepromatous form of leprosy in Medieval England (10 th –12 th centuries AD) to assess whether the individuals buried with the disease were non-locals, possibly from further afield. Enamel samples from 19 individuals from the St. Mary Magdalen Leprosy Hospital, Winchester (UK) were selected for strontium ( 87 Sr/ 86 6U DQG R[\JHQ į 18 O) stable isotope analysis based on age at death (<30 years), the presence of bone changes associated with lepromatous leprosy, and the underlying geology of their burial locations. The results from these data indicate that the St. Mary Magdalen Leprosy Hospital received an almost equal mixture of local and non-local individuals from further afield, including early pilgrims. At present, the St. Mary Magdalen Leprosy Hospital is the earliest dedicated leprosaria found within Britain and mobility studies such as these can help elucidate and test some of the broader historical notions and identities associated with the movements of those infected with the disease in Medieval England.

Trabecular bone architecture in the thumb of recent Homo sapiens, Pan, and Late Pleistocene Homo: Taxonomic differences and evidence for handedness.

The statistics of error and uncertainty are intertwined with ascertaining the admissibility of forensic evidence in a court of law. This issue was especially examined in the 2009 National Academy of Science review of forensic practice. In the analysis of unidentified skeletal remains it is, thus, crucial to formulate a biological profile that gives not only stated errors, but also accuracy and precision of the raw data. In particular, the most accurate biological profile is achieved by using contemporary population-specific standards.S AAPA PRESENTATIONS Crossing disciplines to challenge the adaptationist paradigm. REBECCA R. ACKERMANN. Department of Archaeology, University of Cape Town. In the wake of the Modern Synthesis, Sherwood Washburn’s appeal for a new physical anthropology explicitly called for a shift towards a process-oriented view of evolution. Like others at the time, Washburn overwhelmingly emphasized the role that selection plays in shaping diversity, and biological anthropologists soon began to embrace the idea of interpreting human variation and evolution in terms of underlying selective processes. Today, explanations for phenotypic variation in human evolution remain largely functional/adaptive, despite the strong challenges to the adaptationist paradigm mounted outside of biological anthropology in the past few decades. In this paper, I will discuss our current understanding of the important role that random genetic drift and gene flow have played in shaping phenotypic diversity in hominins. This fuller understanding of the underlying processes responsible for variation has necessitated engaging with other disciplines (e.g. evolutionary biology, quantitative genetics). We have much to gain from modifying the methodological approaches and theoretical developments within those disciplines to our own ends, including a more sophisticated interpretation of the fossil record. As one example, the emerging genomic evidence for gene flow among archaic human populations (e.g. Neanderthals, Denisovans) might have been less surprising (to those for whom it was a surprise) were it not for methodological approaches couched within a lingering adaptationist perspective that has failed to provide a sufficiently nuanced understanding of the evolutionary prevalence and phenotypic consequences of the ‘other’ evolutionary forces. Research funded by the National Research Foundation of South Africa and the University of Cape Town. Effects of predator presence on the behavior of bald-faced saki monkeys (Pithecia irrorata) in the Peruvian Amazon. DARA B. ADAMS, DAWN M. KITCHEN and ASHLEY HURST. Anthropology, The Ohio State University, Anthropology, The University of Texas at San Antonio. Predation is an important selective pressure on prey populations but its influence on primate evolution remains hotly debated. While some researchers argue predation has little effect on group-living in primates, others maintain that constant threats of death strongly impact behavior. Here, we explore the effects of predator presence on saki monkey (Pithecia irrorata) behavior. We hypothesized that saki monkey behavior would differ in high and low use predator areas. Data were collected from June to July 2012 at Centro de Investigación y Capacitación Río Los Amigos in Peru. Over 78 hours of scan and focal sampling were collected on 8 saki monkeys. During 10-minute focal follows, we recorded activity, canopy height, intragroup spacing, vigilance, and number of alarm calls emitted. To determine high and low use predator areas, we conducted a 30-day camera trap survey within the focal group’s home range. During 30 trap nights, we documented four felid species (jaguar, puma, ocelot, and margay) on 11 separate occasions. Camera trap data indicates a pattern of higher predator densities within parts of the sakis’ home range. Analyses of behavioral data suggest that sakis maintain closer associations and engage in less rest and social behavior in high predator areas (Chi-square: P<0.05). However, alarm calling and canopy height are not associated with predator presence (Chi-square: P>0.05). Surprisingly, individuals seem to exhibit less vigilance in high predator areas, which may be related to habitat differences. Our future research will include an assessment of factors such as habitat quality and seasonality on antipredator behavior. Predicting impact stiffness and rate of loading during human walking and heel-strike running. BRIAN J. ADDISON and DANIEL E. LIEBERMAN. Human Evolutionary Biology, Harvard University. Heel-striking during human walking and running generates impacts beneath the foot. These impacts produce large forces over short time periods and occur millions of times per foot per year. In order to understand how the human body evolved to cope with these repetitive impacts, we must first understand how impact force parameters are generated beneath the foot in walking and running. Therefore, we used mass-spring models to predict stiffness and the rate of loading during the impact phase of gait. These models were tested on 20 human subjects walking and running on a rigid surface and four substrates of varying stiffnesses. All subjects walked and ran at Froude numbers of 0.28 and 1.2, respectively. Three-dimensional kinematic and kinetic data were collected using Qualysis motion capture software and an instrumented treadmill. Results indicate that impact stiffness on various substrates can be predicted accurately using knowledge of substrate stiffness and impact stiffness measured a rigid surface. Results also indicate that rate of loading scales predictably with impact stiffness. Importantly, declines in substrate stiffness of 94% produce only 17% declines in impact stiffness during walking compared to 55% declines in impact stiffness during running. This finding suggests that the human foot plays a greater role than substrate in governing impact forces during walking compared to heel-strike running. The performance differences in walking versus running provide a biomechanical context for interpreting morphological changes thought to be related to resisting impact forces, including variations in hominin calcaneal morphology. Funding for this study was provided by Hintze Charitable Foundation and VibramUSA Microfractures in elderly ribs: Contributions to bone quality. AMANDA M. AGNEW, SAM D. STOUT and PAUL W. SCIULLI. Division of Anatomy, The Ohio State University, Department of Anthropology, The Ohio State

Improving Our Understanding of Earth System Processes: GREENCYCLES Annual Network and Midterm Review Meeting, Barcelona, Spain, 21–23 March 2007

The latest Intergovernmental Panel on Climate Change report documents numerous examples of how human activities are profoundly affecting our global environment with long-term consequences for the climate system. However, considerable uncertainty remains concerning future Earth system responses and likely impacts on the sustainability of life on Earth under the threat of changing climate. The International Geosphere-Biosphere Programme recognizes that understanding and quantifying the complex interactions between the biosphere and the climate system are essential for assessing potential sustainable futures. Major limits to our current understanding of biosphere-climate feedbacks result from (1) a lack of observations on biosphere-atmosphere fluxes of important radiatively active gases and aerosols; (2) insufficient mechanistic understanding of the processes driving these exchanges over different temporal and spatial scales; (3) a lack of Earth system models adequately constrained to predict these exchanges as a function of environmental change; and (4) a lack of integration between scientific disciplines and research centers.